Transmission timing control for D2D communication

ABSTRACT

The present invention relates to a transmitting terminal for transmitting data to a receiving terminal over a direct link connection. The transmitting terminal comprises a receiving unit that receives from the base station a timing command for adjusting an uplink transmission timing value for data transmissions to the base station. A generating unit generates direct link timing information, based on the uplink transmission timing value, the direct link timing information being usable for generating a direct link transmission timing value for determining the timing of the data transmission over the direct link. A transmitting unit transmits to the receiving terminal the generated direct link timing information, the direct link timing information being usable at the receiving terminal for generating a direct link reception timing value for determining the reception timing of data to be received on the direct link from the transmitting terminal.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for determiningthe transmission timing of a direct link data transmission in a D2Dcommunication system. In particular, the present invention also relatesto a user equipment capable of operating in a device to devicecommunication system and capable performing the method of the invention.

TECHNICAL BACKGROUND

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support to the next decade. Theability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (Rel. 8 LTE). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM) based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP), and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmission power of the user equipment(UE). Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniques,and a highly efficient control signaling structure is achieved in Rel. 8LTE.

LTE and E-UTRAN Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2.

As can be seen in FIG. 1, the LTE architecture supports interconnectionof different radio access networks (RAN) such as UTRAN or GERAN (GSMEDGE Radio Access Network), which are connected to the EPC via theServing GPRS Support Node (SGSN). In a 3GPP mobile network, the mobileterminal 110 (called User Equipment, UE, or device) is attached to theaccess network via the Node B (NB) in the UTRAN and via the evolved NodeB (eNB) in the E-UTRAN access. The NB and eNB 120 entities are known asbase station in other mobile networks. There are two data packetgateways located in the EPS for supporting the UE mobility—ServingGateway (SGW) 130 and Packet Data Network Gateway 160 (PDN-GW or shortlyPGW). Assuming the E-UTRAN access, the eNB entity 120 may be connectedthrough wired lines to one or more SGWs via the S1-U interface (“U”stays for “user plane”) and to the Mobility Management Entity 140 (MME)via the S1-MMME interface. The SGSN 150 and MME 140 are also referred toas serving core network (CN) nodes.

As depicted in FIG. 2, the E-UTRAN consists of evolved Node B (eNBs)120, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and controlplane (RRC) protocol terminations towards the UE. The eNB 120 hosts thePhysical (PHY), Medium Access Control (MAC), Radio Link Control (RLC),and Packet Data Control Protocol (PDCP) layers that include thefunctionality of user-plane header-compression and encryption. It alsooffers Radio Resource Control (RRC) functionality corresponding to thecontrol plane. It performs many functions including radio resourcemanagement, admission control, scheduling, enforcement of negotiated ULQoS, cell information broadcast, ciphering/deciphering of user andcontrol plane data, and compression/decompression of DL/UL user planepacket headers.

The eNBs are interconnected with each other by means of the X2interface. The eNBs are also connected by means of the S1 interface tothe EPC (Evolved Packet Core), more specifically to the MME (MobilityManagement Entity) by means of the S1-MME and to the Serving Gateway(S-GW) by means of the S1-U. The S1 interface supports a many-to-manyrelation between MMEs/Serving Gateways and eNBs. The SGW routes andforwards user data packets, while also acting as the mobility anchor forthe user plane during inter-eNB handovers and as the anchor for mobilitybetween LTE and other 3GPP technologies (terminating S4 interface andrelaying the traffic between 2G/3G systems and PDN GW). For idle stateUEs, the SGW terminates the DL data path and triggers paging when DLdata arrives for the UE. It manages and stores UE contexts, e.g.parameters of the IP bearer service, network internal routinginformation. It also performs replication of the user traffic in case oflawful interception.

The MME 140 is the key control-node for the LTE access-network. It isresponsible for idle mode UE tracking and paging procedure includingretransmissions. It is involved in the bearer activation/deactivationprocess and is also responsible for choosing the SGW for a UE at theinitial attach and at time of intra-LTE handover involving Core Network(CN) node relocation. It is responsible for authenticating the user (byinteracting with the HSS). The Non-Access Stratum (NAS) signalingterminates at the MME and it is also responsible for generation andallocation of temporary identities to UEs. It checks the authorizationof the UE to camp on the service provider's Public Land Mobile Network(PLMN) and enforces UE roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roamingUEs.

Component Carrier Structure in LTE

FIGS. 3 and 4 illustrate the structure of a component carrier in LTE.The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called sub-frames. In 3GPP LTE eachsub-frame is divided into two downlink slots as shown in FIG. 3, whereinthe first downlink slot comprises the control channel region (PDCCHregion) within the first OFDM symbols. Each sub-frame consists of a givenumber of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPPLTE (Release 8)), wherein each of OFDM symbol spans over the entirebandwidth of the component carrier. The OFDM symbols thus each consistof a number of modulation symbols transmitted on respective N_(RB)^(DL)×N_(sc) ^(RB) subcarriers as also shown in FIG. 4.

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block is defined as N_(symb) ^(DL) consecutive OFDMsymbols in the time domain and N_(sc) ^(RB) consecutive subcarriers inthe frequency domain as exemplified in FIG. 4. In 3GPP LTE (Release 8),a physical resource block thus consists of N_(symb) ^(DL)×N_(sc) ^(RB)resource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (further details on the downlink resourcegrid can be found, for example, in 3GPP TS 36.211, “Evolved universalterrestrial radio access (E-UTRA); physical channels and modulations(Release 10)”, version 10.4.0, 2011, Section 6.2, freely available atwww.3gpp.org, which is incorporated herein by reference).

While it can happen that some resource elements within a resource blockor resource block pair are not used even though it has been scheduled,for simplicity of the used terminology still the whole resource block orresource block pair is assigned. Examples for resource elements that areactually not assigned by a scheduler include reference signals,broadcast signals, synchronization signals, and resource elements usedfor various control signal or channel transmissions.

The number of physical resource blocks in downlink depends on thedownlink transmission bandwidth configured in the cell and is at presentdefined in LTE as being from the interval of 6 to 110 (P)RBs. It iscommon practice in LTE to denote the bandwidth either in units of Hz(e.g. 10 MHz) or in units of resource blocks, e.g. for the downlink casethe cell bandwidth can equivalently expressed as e.g. 10 MHz or.

A channel resource may be defined as a “resource block” as exemplaryillustrated in FIG. 3 where a multi-carrier communication system, e.g.employing OFDM as for example discussed in the LTE work item of 3GPP, isassumed. More generally, it may be assumed that a resource blockdesignates the smallest resource unit on an air interface of a mobilecommunication that can be assigned by a scheduler. The dimensions of aresource block may be any combination of time (e.g. time slot, subframe,frame, etc. for time division multiplex (TDM)), frequency (e.g. subband,carrier frequency, etc. for frequency division multiplex (FDM)), code(e.g. spreading code for code division multiplex (CDM)), antenna (e.g.Multiple Input Multiple Output (MIMO)), etc. depending on the accessscheme used in the mobile communication system.

The data are mapped onto physical resource blocks by means of pairs ofvirtual resource blocks. A pair of virtual resource blocks is mappedonto a pair of physical resource blocks. The following two types ofvirtual resource blocks are defined according to their mapping on thephysical resource blocks in LTE downlink: Localized Virtual ResourceBlock (LVRB) and Distributed Virtual Resource Block (DVRB). In thelocalized transmission mode using the localized VRBs, the eNB has fullcontrol which and how many resource blocks are used, and should use thiscontrol usually to pick resource blocks that result in a large spectralefficiency. In most mobile communication systems, this results inadjacent physical resource blocks or multiple clusters of adjacentphysical resource blocks for the transmission to a single userequipment, because the radio channel is coherent in the frequencydomain, implying that if one physical resource block offers a largespectral efficiency, then it is very likely that an adjacent physicalresource block offers a similarly large spectral efficiency. In thedistributed transmission mode using the distributed VRBs, the physicalresource blocks carrying data for the same UE are distributed across thefrequency band in order to hit at least some physical resource blocksthat offer a sufficiently large spectral efficiency, thereby obtainingfrequency diversity.

In 3GPP LTE Release 8 the downlink control signaling is basicallycarried by the following three physical channels:

Physical control format indicator channel (PCFICH) for indicating thenumber of OFDM symbols used for control signaling in a subframe (i.e.the size of the control channel region);

Physical hybrid ARQ indicator channel (PHICH) for carrying the downlinkACK/NACK associated with uplink data transmission; and

Physical downlink control channel (PDCCH) for carrying downlinkscheduling assignments and uplink scheduling assignments.

The PCFICH is sent from a known position within the control signalingregion of a downlink subframe using a known pre-defined modulation andcoding scheme. The user equipment decodes the PCFICH in order to obtaininformation about a size of the control signaling region in a subframe,for instance, the number of OFDM symbols. If the user equipment (UE) isunable to decode the PCFICH or if it obtains an erroneous PCFICH value,it will not be able to correctly decode the L1/L2 control signaling(PDCCH) comprised in the control signaling region, which may result inlosing all resource assignments contained therein.

The PDCCH carries control information, such as, for instance, schedulinggrants for allocating resources for downlink or uplink datatransmission. The PDCCH for the user equipment is transmitted on thefirst of either one, two or three OFDM symbols according to PCFICHwithin a subframe.

Physical downlink shared channel (PDSCH) is used to transport user data.PDSCH is mapped to the remaining OFDM symbols within one subframe afterPDCCH. The PDSCH resources allocated for one UE are in the units ofresource block for each subframe.

Physical uplink shared channel (PUSCH) carries user data. PhysicalUplink Control Channel (PUCCH) carries signaling in the uplink directionsuch as scheduling requests, HARQ positive and negative acknowledgementsin response to data packets on PDSCH, and channel state information(CSI).

The term “component carrier” refers to a combination of several resourceblocks. In future releases of LTE, the term “component carrier” is nolonger used; instead, the terminology is changed to “cell”, which refersto a combination of downlink and optionally uplink resources. Thelinking between the carrier frequency of the downlink resources and thecarrier frequency of the uplink resources is indicated in the systeminformation transmitted on the downlink resources.

Further Advancements for LTE (LTE-A)

The frequency spectrum for International MobileTelecommunications-Advanced (IMT-Advanced) was decided at the WorldRadio communication Conference 2007 (WRC-07). Although the overallfrequency spectrum for IMT-Advanced was decided, the actual availablefrequency bandwidth is different according to each region or country.Following the decision on the available frequency spectrum outline,however, standardization of a radio interface started in the 3rdGeneration Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting,the Study Item description on “Further Advancements for E-UTRA(LTE-Advanced)” was approved in the 3GPP. The study item coverstechnology components to be considered for the evolution of E-UTRA, e.g.to fulfill the requirements on IMT-Advanced. Two major technologycomponents which are currently under consideration for LTE-A aredescribed in the following.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers (CCs) areaggregated in order to support wider transmission bandwidths up to 100MHz. Several cells in the LTE system are aggregated into one widerchannel in the LTE-Advanced system which is wide enough for 100 MHz,even though these cells in LTE are in different frequency bands. A UEmay simultaneously receive or transmit on one or multiple CCs dependingon its capabilities:

-   -   A Rel-10 UE with reception and/or transmission capabilities for        CA can simultaneously receive and/or transmit on multiple CCs        corresponding to multiple serving cells;    -   A Rel-8/9 UE can receive on a single CC and transmit on a single        CC corresponding to one serving cell only.

Carrier aggregation (CA) is supported for both contiguous andnon-contiguous CCs with each CC limited to a maximum of 110 ResourceBlocks in the frequency domain using the Rel-8/9 numerology.

It is possible to configure a user equipment to aggregate a differentnumber of component carriers originating from the same eNodeB (basestation) and of possibly different bandwidths in the uplink and thedownlink. The number of downlink component carriers that can beconfigured depends on the downlink aggregation capability of the UE.Conversely, the number of uplink component carriers that can beconfigured depends on the uplink aggregation capability of the UE. Itmay not be possible to configure a mobile terminal with more uplinkcomponent carriers than downlink component carriers.

In a typical TDD deployment, the number of component carriers and thebandwidth of each component carrier in uplink and downlink is the same.Component carriers originating from the same eNodeB need not to providethe same coverage.

Component carriers shall be LTE Rel-8/9 compatible. Nevertheless,existing mechanisms (e.g. barring) may be used to avoid Rel-8/9 UEs tocamp on a component carrier.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time preserve orthogonally of the subcarriers with15 kHz spacing. Depending on the aggregation scenario, the n×300 kHzspacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

The Layer 2 structure with activated carrier aggregation is shown inFIG. 5 and FIG. 6 for the downlink and uplink respectively. Thetransport channels are described between MAC and Layer 1, the logicalchannels are described between MAC and RLC.

When carrier aggregation (CA) is configured, the UE only has one RRCconnection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides theNAS mobility information (e.g. TAI), and at RRC connectionre-establishment/handover, one serving cell provides the security input.This cell is referred to as the Primary Cell (PCell). In the downlink,the carrier corresponding to the PCell is the Downlink Primary ComponentCarrier (DL PCC) while in the uplink it is the Uplink Primary ComponentCarrier (UL PCC).

Depending on UE capabilities, Secondary Cells (SCells) can be configuredto form together with the PCell a set of serving cells. In the downlink,the carrier corresponding to an SCell is a Downlink Secondary ComponentCarrier (DL SCC), while in the uplink it is an Uplink SecondaryComponent Carrier (UL SCC).

The configured set of serving cells for a UE therefore always consistsof one PCell and one or more SCells:

-   -   For each SCell the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCCs and no SCell can be configured for usage of        uplink resources only);    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell;    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE;    -   PCell can only be changed with handover procedure (i.e. with        security key change and RACH procedure);    -   PCell is used for transmission of PUCCH;    -   Unlike SCells, PCell cannot be de-activated;    -   Re-establishment is triggered when the PCell experiences        Rayleigh fading (RLF), not when SCells experience RLF;    -   Non-access stratum (NAS) information is taken from the downlink        PCell; The configuration and reconfiguration of component        carriers can be performed by RRC.

Activation and deactivation is done via MAC control elements. Atintra-LTE handover, RRC can also add, remove, or reconfigure SCells forusage in the target cell. The reconfiguration, addition and removal ofSCells can be performed by RRC. At intra-LTE handover, RRC can also add,remove, or reconfigure SCells for usage with the target PCell. Whenadding a new SCell, dedicated RRC signaling is used for sending allrequired system information of the SCell i.e. while in connected mode,UEs need not acquire broadcasted system information directly from theSCells.

When a user equipment is configured with carrier aggregation there isone pair of uplink and downlink component carriers that is alwaysactive. The downlink component carrier of that pair might be alsoreferred to as ‘DL anchor carrier’. Same applies also for the uplink.

When carrier aggregation is configured, a user equipment may bescheduled over multiple component carriers simultaneously but at mostone random access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI formats, calledCIF.

A linking between uplink and downlink component carriers allowsidentifying the uplink component carrier for which the grant applieswhen there is no-cross-carrier scheduling. The linkage of downlinkcomponent carriers to uplink component carrier does not necessarily needto be one to one. In other words, more than one downlink componentcarrier can link to the same uplink component carrier. At the same time,a downlink component carrier can only link to one uplink componentcarrier.

LTE RRC States

The following is mainly describing the two main states in LTE:“RRC_IDLE” and “RRC_CONNECTED”.

In RRC_IDLE the radio is not active, but an ID is assigned and trackedby the network. More specifically, a mobile terminal in RRC_IDLEperforms cell selection and reselection—in other words, it decides onwhich cell to camp. The cell (re)selection process takes into accountthe priority of each applicable frequency of each applicable RadioAccess Technology (RAT), the radio link quality and the cell status(i.e. whether a cell is barred or reserved). An RRC_IDLE mobile terminalmonitors a paging channel to detect incoming calls, and also acquiressystem information. The system information mainly consists of parametersby which the network (E-UTRAN) can control the cell (re)selectionprocess. RRC specifies the control signalling applicable for a mobileterminal in RRC_IDLE, namely paging and system information. The mobileterminal behaviour in RRC_IDLE is specified in TR 25.912, e.g. Chapter8.4.2 incorporate herein by reference.

In RRC_CONNECTED the mobile terminal has an active radio operation withcontexts in the eNodeB. The E-UTRAN allocates radio resources to themobile terminal to facilitate the transfer of (unicast) data via shareddata channels. To support this operation, the mobile terminal monitorsan associated control channel which is used to indicate the dynamicallocation of the shared transmission resources in time and frequency.The mobile terminal provides the network with reports of its bufferstatus and of the downlink channel quality, as well as neighbouring cellmeasurement information to enable E-UTRAN to select the most appropriatecell for the mobile terminal. These measurement reports include cellsusing other frequencies or RATs. The UE also receives systeminformation, consisting mainly of information required to use thetransmission channels. To extend its battery lifetime, a UE inRRC_CONNECTED may be configured with a Discontinuous Reception (DRX)cycle. RRC is the protocol by which the E-UTRAN controls the UEbehaviour in RRC_CONNECTED.

Uplink Access Scheme for LTE

For Uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and assumed improvedcoverage (higher data rates for a given terminal peak power). Duringeach time interval, Node B assigns users a unique time/frequencyresource for transmitting user data thereby ensuring intra-cellorthogonality. An orthogonal access in the uplink promises increasedspectral efficiency by eliminating intra-cell interference. Interferencedue to multipath propagation is handled at the base station (Node B),aided by insertion of a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BWgrant during one time interval, e.g. asub-frame of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a sub-frame, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is however possible to assign a frequency resourceBWgrant over a longer time period than one TTI to a user byconcatenation of sub-frames.

Uplink Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines

-   -   which UE(s) that is (are) allowed to transmit,    -   which physical channel resources (frequency),    -   Transport format (Modulation Coding Scheme (MCS)) to be used by        the mobile terminal for transmission

The allocation information is signaled to the UE via a scheduling grant,sent on the L1/L2 control channel. For simplicity reasons this channelis called uplink grant channel in the following. A scheduling grantmessage contains at least information which part of the frequency bandthe UE is allowed to use, the validity period of the grant, and thetransport format the UE has to use for the upcoming uplink transmission.The shortest validity period is one sub-frame. Additional informationmay also be included in the grant message, depending on the selectedscheme. Only “per UE” grants are used to grant the right to transmit onthe UL-SCH (i.e. there are no “per UE per RB” grants). Therefore the UEneeds to distribute the allocated resources among the radio bearersaccording to some rules, which will be explained in detail in one of thenext sections. Unlike in HSUPA there is no UE based transport formatselection. The eNB decides the transport format based on someinformation, e.g. reported scheduling information and QoS info, and UEhas to follow the selected transport format.

Buffer Status Reporting/Scheduling Request Procedure for UplinkScheduling

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesubframes. They are transmitted on the PDCCH using C-RNTI of the UE asalready mentioned before. Dynamic scheduling is efficient for servicestypes, in which the traffic is bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one subframe, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each subframe. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Buffer status reports (BSR) from the UE to the eNB are used to assistthe eNodeB in allocating uplink resources, i.e. uplink scheduling asexplained in more in detail in [2]. For the downlink case the eNBscheduler is obviously aware of the amount of data to be delivered toeach UE, however for the uplink direction since scheduling decisions aredone at the eNB and the buffer for the data is in the UE, BSRs have tobe sent from UE to the eNB in order to indicate the amount of data thatneeds to be transmitted over UL-SCH.

There are basically two types of BSR defined for LTE: a long BSR and ashort BSR. Which one is transmitted by the UE depends on the availabletransmission resources in a transport block, on how many groups oflogical channels have non-empty buffer, and on whether a specific eventis triggered at the UE. The long BSR reports the amount of data for fourlogical channel groups, whereas the short BSR indicates only the amountof data buffered for the highest logical channel group. The reason forintroducing the logical channel group concept is that even though the UEmay have more than four logical channels configured reporting the bufferstatus for each individual logical channel would cause too muchsignalling overhead. Therefore eNB assigns each logical channel to alogical channel group; preferably logical channels with the same/similarQoS requirements should be allocated within the same logical channelgroup.

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

A BSR may be triggered, as an example, for the following events:

-   -   Whenever data arrives for a logical channel, which has a higher        priority than the logical channels whose buffer are non-empty;    -   Whenever data becomes available for any logical channel, when        there was previously no data available for transmission;    -   Whenever the retransmission BSR time expires;    -   Whenever periodic BSR reporting is due, i.e. periodic BSR timer        expires;    -   Whenever there is a spare space in a transport block which can        accommodate a BSR.

In order to be robust against transmission failures there is a BSRretransmission mechanism defined for LTE; the retransmission BSR timeris started or restarted whenever an uplink grant is received. If nouplink grant is received before the timer expires another BSR istriggered by the UE.

If the UE has no uplink resources allocated for including a BSR in theTB when a BSR is triggered the UE sends a scheduling request (SR) on thePhysical Uplink Control Channel (PUCCH) if configured. For the case thatthere are no D-SR (dedicated Scheduling request) resources on PUCCHconfigured UE will start the Random Access Procedure (RACH procedure) inorder to request UL-SCH resources for transmission the BSR info to eNB.However it should be noted that the UE will not trigger SR transmissionfor the case that a periodic BSR is to be transmitted.

Furthermore an enhancement to the SR transmission has been introducedfor a specific scheduling mode where resources are persistentlyallocated with a defined periodicity in order to save L1/2 controlsignalling overhead for transmission grants, which is referred to assemi-persistent scheduling (SPS). One example for a service, which hasbeen mainly considered for semi-persistent scheduling is VoIP. Every 20ms a VoIP packets is generated at the Codec during a talk-spurt.Therefore eNB can allocate uplink or respectively downlink resourcepersistently every 20 ms, which could be then used for the transmissionof VoIP packets. In General SPS is beneficial for services withpredictable traffic behaviour, i.e. constant bit rate, packet arrivaltime is periodic. For the case that SPS is configured for the uplinkdirection, the eNB can turn off SR triggering/transmission for certainconfigured logical channels, i.e. BSR triggering due to data arrival onthose specific configured logical channels will not trigger an SR. Themotivation for such kind of enhancements is reporting an SR for thoselogical channels which will use the semi-persistently allocatedresources (logical channels which carry VoIP packets) is of no value foreNB scheduling and hence should be avoided.

More detailed information with regard to BSR procedures and inparticular the triggering of same is explained in 3GPP TS 36.321 V10.5in Chapter 5.4.5 incorporated herewith by reference.

Logical Channel Prioritization

The UE has an uplink rate control function which manages the sharing ofuplink resources between radio bearers. This uplink rate controlfunction is also referred to as logical channel prioritization procedurein the following. The Logical Channel Prioritization (LCP) procedure isapplied when a new transmission is performed, i.e. a Transport blockneeds to be generated. One proposal for assigning capacity has been toassign resources to each bearer, in priority order, until each hasreceived an allocation equivalent to the minimum data rate for thatbearer, after which any additional capacity is assigned to bearers in,for example, priority order.

As will become evident from the description of the LCP procedure givenbelow, the implementation of the LCP procedure residing in the UE isbased on the token bucket model, which is well known in the IP world.The basic functionality of this model is as follows. Periodically at agiven rate a token, which represents the right to transmit a quantity ofdata, is added to the bucket. When the UE is granted resources, it isallowed to transmit data up to the amount represented by the number oftokens in the bucket. When transmitting data the UE removes the numberof tokens equivalent to the quantity of transmitted data. In case thebucket is full, any further tokens are discarded. For the addition oftokens it could be assumed that the period of the repetition of thisprocess would be every TTI, but it could be easily lengthened such thata token is only added every second. Basically instead of every 1 ms atoken is added to the bucket, 1000 tokens could be added every second.In the following the logical channel prioritization procedure which isused in Rel-8 is described [TS 36.321]. More detailed information withregard to the LCP procedure is explained in 3GPP TS 36.321 V8 in Chapter5.4.3.1, incorporated herewith by reference.

RRC controls the scheduling of uplink data by signalling for eachlogical channel: priority where an increasing priority value indicates alower priority level, prioritised BitRate which sets the Prioritized BitRate (PBR), bucketSizeDuration which sets the Bucket Size Duration(BSD). The idea behind prioritized bit rate is to support for eachbearer, including low priority non-GBR bearers, a minimum bit rate inorder to avoid a potential starvation. Each bearer should at least getenough resources in order to achieve the prioritized bit rate (PRB).

The UE shall maintain a variable Bj for each logical channel j. Bj shallbe initialized to zero when the related logical channel is established,and incremented by the product PBR×TTI duration for each TTI, where PBRis Prioritized Bit Rate of logical channel j. However, the value of Bjcan never exceed the bucket size and if the value of Bj is larger thanthe bucket size of logical channel j, it shall be set to the bucketsize. The bucket size of a logical channel is equal to PBR×BSD, wherePBR and BSD are configured by upper layers.

The UE shall perform the following Logical Channel Prioritizationprocedure when a new transmission is performed:

-   -   The UE shall allocate resources to the logical channels in the        following steps:        -   Step 1: All the logical channels with Bj>0 are allocated            resources in a decreasing priority order. If the PBR of a            radio bearer is set to “infinity”, the UE shall allocate            resources for all the data that is available for            transmission on the radio bearer before meeting the PBR of            the lower priority radio bearer(s);        -   Step 2: the UE shall decrement Bj by the total size of MAC            SDUs served to logical channel j in Step 1.

It has to be noted at this point that the value of Bj can be negative.

-   -   Step 3: if any resources remain, all the logical channels are        served in a strict decreasing priority order (regardless of the        value of Bj) until either the data for that logical channel or        the UL grant is exhausted, whichever comes first. Logical        channels configured with equal priority should be served        equally.    -   The UE shall also follow the rules below during the scheduling        procedures above:        -   the UE should not segment an RLC SDU (or partially            transmitted SDU or retransmitted RLC PDU) if the whole SDU            (or partially transmitted SDU or retransmitted RLC PDU) fits            into the remaining resources;        -   if the UE segments an RLC SDU from the logical channel, it            shall maximize the size of the segment to fill the grant as            much as possible;        -   UE should maximise the transmission of data.

For the Logical Channel Prioritization procedure, the UE shall take intoaccount the following relative priority in decreasing order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

For the case of carrier aggregation, which is described in a latersection, when the UE is requested to transmit multiple MAC PDUs in oneTTI, steps 1 to 3 and the associated rules may be applied either to eachgrant independently or to the sum of the capacities of the grants. Alsothe order in which the grants are processed is left up to UEimplementation. It is up to the UE implementation to decide in which MACPDU a MAC control element is included when UE is requested to transmitmultiple MAC PDUs in one TTI.

Uplink Power Control

Uplink transmission power control in a mobile communication systemserves an important purpose: it balances the need for sufficienttransmitted energy per bit to achieve the required Quality-of-Service(QoS), against the needs to minimize interference to other users of thesystem and to maximize the battery life of the mobile terminal. Inachieving this purpose, the role of the Power Control (PC) becomesdecisive to provide the required SINR while controlling at the same timethe interference caused to neighbouring cells. The idea of classic PCschemes in uplink is that all users are received with the same SINR,which is known as full compensation. As an alternative, 3GPP has adoptedfor LTE the use of Fractional Power Control (FPC). This newfunctionality makes users with a higher path-loss operate at a lowerSINR requirement so that they will more likely generate lessinterference to neighbouring cells.

Detailed power control formulae are specified in LTE for the PhysicalUplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH)and the Sounding Reference Signals (SRSs) (section 5.1 in TS 36.213).The formula for each of these uplink signals follows the same basicprinciples; in all cases they can be considered as a summation of twomain terms: a basic open-loop operating point derived from static orsemi-static parameters signalled by the eNodeB, and a dynamic offsetupdated from subframe to subframe.

The basic open-loop operating point for the transmit power per resourceblock depends on a number of factors including the inter-cellinterference and cell load. It can be further broken down into twocomponents, a semi-static base level P0, further comprised of a commonpower level for all UEs in the cell (measured in dBm) and a UE-specificoffset, and an open-loop path-loss compensation component. The dynamicoffset part of the power per resource block can also be further brokendown into two components, a component dependent on the used MCS andexplicit Transmitter Power Control (TPC) commands.

The MCS-dependent component (referred to in the LTE specifications as,where TF stands for ‘Transport Format’) allows the transmitted power perRB to be adapted according to the transmitted information data rate.

The other component of the dynamic offset is the UE-specific TPCcommands. These can operate in two different modes: accumulative TPCcommands (available for PUSCH, PUCCH and SRS) and absolute TPC commands(available for PUSCH only). For the PUSCH, the switch between these twomodes is configured semi-statically for each UE by RRC signalling—i.e.the mode cannot be changed dynamically. With the accumulative TPCcommands, each TPC command signals a power step relative to the previouslevel.

Timing Advance

For the uplink transmission scheme of LTE single-carrier frequencydivision multiple access (SC-FDMA) was chosen to achieve an orthogonalmultiple-access in time and frequency between the different UEstransmitting in the uplink.

Uplink orthogonality is maintained by ensuring that the transmissionsfrom different UEs in a cell are time-aligned at the receiver of theeNB. This avoids intracell interference occurring, both between UEsassigned to transmit in consecutive subframes and between UEstransmitting on adjacent subcarriers. Time alignment of the uplinktransmissions is achieved by applying a timing advance at the UEtransmitter, relative to the received downlink timing. This isillustrated in FIG. 5. The main role of this is to counteract differingpropagation delays between different UEs.

Timing Advance Procedure

When UE is synchronized to the downlink transmissions received from eNB,the initial timing advance is set by means of the random accessprocedure. This involves the UE transmitting a random access preamblefrom which the eNodeB can estimate the uplink timing and respond with an11-bit initial timing advance command contained within the Random AccessResponse (RAR) message. This allows the timing advance to be configuredby the eNodeB with a granularity of 0.52 μs from 0 up to a maximum of0.67 ms.

Once the timing advance has been first set for each user equipment, thetiming advance is updated from time to time to counteract changes in thearrival time of the uplink signals at the eNodeB. In deriving the timingadvance update commands, the eNodeB may measure any uplink signal whichis useful. The details of the uplink timing measurements at the eNodeBare not specified, but left to the implementation of the eNodeB.

The timing advance update commands are generated at the Medium AccessControl (MAC) layer in the eNodeB and transmitted to the user equipmentas MAC control elements which may be multiplexed together with data onthe Physical Downlink Shared Channel (PDSCH). Like the initial timingadvance command in the response to the Random Access Channel (RACH)preamble, the update commands have a granularity of 0.52 μs. The rangeof the update commands is ±16 μs, allowing a step change in uplinktiming equivalent to the length of the extended cyclic prefix. Theywould typically not be sent more frequently than about every 2 seconds.In practice, fast updates are unlikely to be necessary, as even for auser equipment moving at 500 km/h the change in round-trip path lengthis not more than 278 m/s, corresponding to a change in round-trip timeof 0.93 μs/s.

Upon reception of a timing advance command, the UE shall adjust itsuplink transmission timing for PUCCH/PUSCH/SRS of the primary cell. Thetiming advance command indicates the change of the uplink timingrelative to the current uplink timing as multiples of 16T_(s). The ULtransmission timing for PUSCH/SRS of a secondary cell is the same as theprimary cell.

In case of random access response, 11-bit timing advance command, T_(A),indicates N_(TA) values by index values of T_(A)=0, 1, 2, . . . , 1282,where an amount of the time alignment is given by N_(TA)=T_(A)×16.N_(TA) is defined in [3].

In other cases, 6-bit timing advance command, T_(A), indicatesadjustment of the current N_(TA) value, N_(TA,old), to the new N_(TA)value, N_(TA,new), by index values of T_(A)=0, 1, 2, . . . , 63, whereN_(TA,new)=N_(TA,old)+(T_(A)−31)×16. Here, adjustment of N_(TA) value bya positive or a negative amount indicates advancing or delaying theuplink transmission timing by a given amount respectively.

For a timing advance command received on subframe n, the correspondingadjustment of the timing shall apply from the beginning of subframe n+6.When the UE's uplink PUCCH/PUSCH/SRS transmissions in subframe n andsubframe n+1 are overlapped due to the timing adjustment, the UE shalltransmit complete subframe n and not transmit the overlapped part ofsubframe n+1.

If the received downlink timing changes and is not compensated or isonly partly compensated by the uplink timing adjustment without timingadvance command as specified in TS 36.133, the UE changes N_(TA)accordingly.

The eNodeB balances the overhead of sending regular timing updatecommands to all the UEs in the cell against a UE's ability to transmitquickly when data arrives in its transmit buffer. The eNodeB thereforeconfigures a timer for each user equipment, which the user equipmentrestarts each time a timing advance update is received. This timer isalso referred to as Timing Advance Timer (TAT). In case the userequipment does not receive another timing advance update before thetimer expires, it must then consider that it has lost uplinksynchronization (see also section 5.2 of 3GPP TS 36.321, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC)protocol specification”, version 8.9.0, which is incorporated herein byreference).

In such a case, in order to avoid the risk of generating interference touplink transmissions from other user equipments, the UE is not permittedto make another uplink transmission of any sort.

Additional properties of the timing advance procedure can be found in TS36.321 and TS 36.133 (section 7.1) incorporated herein by reference.

LTE Device to Device (D2D) Proximity Services

Proximity-based applications and services represent an emergingsocial-technological trend. The identified areas include servicesrelated to commercial services and Public Safety that would be ofinterest to operators and users. The introduction of a ProximityServices (ProSe) capability in LTE would allow the 3GPP industry toserve this developing market, and will, at the same time, serve theurgent needs of several Public Safety communities that are jointlycommitted to LTE.

Device-to-Device (D2D) communication is a technology component forLTE-rel.12. The Device-to-Device (D2D) communication technology allowsD2D as an underlay to the cellular network to increase the spectralefficiency. For example, if the cellular network is LTE, all datacarrying physical channels use SC-FDMA for D2D signaling. In D2Dcommunication, user equipments (UEs) transmit data signals to each otherover a direct link using the cellular resources instead of through theBase Station. A possible scenario in a D2D compatible communicationsystem is shown in FIG. 7.

D2D Communication in LTE

The “D2D communication in LTE” is focusing on two areas; Discovery andCommunication whereas this invention is mostly related to the Discoverypart.

Device-to-Device (D2D) communication is a technology component forLTE-A. In D2D communication, UEs transmit data signals to each otherover a direct link using the cellular resources instead of through theBS. D2D users communicate directly while remaining controlled under theBS, i.e. at least when being in coverage of an eNB. Therefore D2D canimprove system performances by reusing cellular resources.

It is assumed that D2D operates in uplink LTE spectrum (in the case ofFDD) or uplink sub-frames of the cell giving coverage (in case of TDDexcept when out of coverage). Furthermore D2D transmission/receptiondoes not use full duplex on a given carrier. From individual UEperspective, on a given carrier D2D signal reception and LTE uplinktransmission do not use full duplex, i.e. no simultaneous D2D signalreception and LTE UL transmission is possible.

In D2D communication when UE1 has a role of transmission (transmittinguser equipment or transmitting terminal), UE1 sends data and UE2(receiving user equipment) receives it. UE1 and UE2 can change theirtransmission and reception role. The transmission from UE1 can bereceived by one or more UEs like UE2.

With respect to the User plane protocols, in the following the contentof the agreement from D2D communication perspective is reported (3GPP TR36.843, version 12.0.0 section 9.2, incorporated herein by reference):

-   -   PDCP:        -   1: M D2D broadcast communication data (i.e. IP packets)            should be handled as the normal user-plane data.        -   Header-compression/decompression in PDCP is applicable for            1: M D2D broadcast communication.            -   U-Mode is used for header compression in PDCP for D2D                broadcast operation for public safety;    -   RLC:        -   RLC UM is used for 1: M D2D broadcast communication.        -   Segmentation and Re-assembly is supported on L2 by RLC UM.        -   A receiving UE needs to maintain at least one RLC UM entity            per transmitting peer UE.        -   An RLC UM receiver entity does not need to be configured            prior to reception of the first RLC UM data unit.        -   So far no need has been identified for RLC AM or RLC TM for            D2D communication for user plane data transmission.    -   MAC:        -   No HARQ feedback is assumed for 1: M D2D broadcast            communication        -   The receiving UE needs to know a source ID in order to            identify the receiver RLC UM entity.        -   The MAC header comprises a L2 target ID which allows            filtering out packets at MAC layer.        -   The L2 target ID may be a broadcast, group cast or unicast            address.            -   L2 Groupcast/Unicast: A L2 target ID carried in the MAC                header would allow discarding a received RLC UM PDU even                before delivering it to the RLC receiver entity.            -   L2 Broadcast: A receiving UE would process all received                RLC PDUs from all transmitters and aim to re-assemble                and deliver IP packets to upper layers.        -   MAC sub header contains LCIDs (to differentiate multiple            logical channels).        -   At least Multiplexing/de-multiplexing, priority handling and            padding are useful for D2D.            Resource Allocation            Radio Resource Allocation

FIG. 9 illustrates the behavior regarding resource allocation in D2Dcommunication. The resource allocation for D2D communication is underdiscussion and is described in its present form in 3GPP TR 36.843,version 12.0.0, section 9.2.3, incorporated herein by reference.

From the perspective of a transmitting UE, a proximity Services enabledUE (ProSe-enabled UE) can operate in two modes for resource allocation:

-   -   Mode 1 (eNB scheduled resource allocation): eNodeB or Release-10        relay node schedules the exact resources used by a UE to        transmit direct data and direct control information. The UE        needs to be RRC_CONNECTED in order to transmit data. Further,        the UE requests transmission resources from the eNB and the eNB        schedules transmission resources for transmission of scheduling        assignment(s) and data. The UE sends a scheduling request (D-SR        or Random Access) to the eNB followed by a BSR. Based on the BSR        the eNB can determine that the UE has data for a ProSe Direct        Communication transmission and estimate the resources needed for        transmission.    -   Mode 2 (UE autonomous resource selection): a UE on its own        selects resources from resource pools to transmit direct data        and direct control information

What resource allocation mode a UE is going to use for D2D datacommunication depends basically on the RRC state, i.e. RRC_IDLE orRRC_CONNECTED, and the coverage state of the UE, i.e. in-coverage,out-of-coverage. A UE is considered in-coverage if it has a serving cell(i.e. the UE is RRC_CONNECTED or is camping on a cell in RRC_IDLE).

Specifically, the following rules with respect to the resourceallocation mode apply for the UE (according to TS 36.300):

-   -   If the UE is out-of-coverage it can only use mode 2;    -   If the UE is in-coverage it may use mode 1 if the eNB configures        it accordingly;    -   If the UE is in-coverage it may use mode 2 if the eNB configures        it accordingly;    -   When there are no exceptional conditions, UE changes from Mode 1        to Mode 2 or mode 2 to mode 1 only if it is configured by eNB to        do so. If the UE is in-coverage it shall use only the mode        indicated by eNB configuration unless one of the exceptional        cases occurs;    -   The UE considers itself to be in exceptional conditions while        T311 or T301 is running;    -   When an exceptional case occurs the UE is allowed to use mode 2        temporarily even though it was configured to use mode 1.

While being in the coverage area of an E-UTRA cell, the UE shall onlyperform ProSe Direct Communication Transmission on the UL carrier onlyon the resources assigned by that cell, even if resources of thatcarrier have been pre-configured e.g. in UICC.

For UEs in RRC_IDLE UEs the eNB may select one of the following options:

-   -   The eNB may provide a Mode 2 transmission resource pool in SIB.        UEs that are authorized for Prose Direct Communication use these        resources for ProSe Direct Communication in RRC_IDLE;    -   The eNB may indicate in SIB that it supports D2D but does not        provide resources for ProSe Direct Communication. UEs need to        enter RRC_CONNECTED to perform ProSe Direct Communication        transmission.

For UEs in RRC_CONNECTED:

-   -   A UE in RRC_CONNECTED that is authorized to perform ProSe Direct        Communication transmission, when it needs to perform ProSe        Direct Communication transmission indicates to the eNB that it        wants to perform ProSe Direct Communication transmissions;    -   The eNB validates whether the UE in RRC_CONNECTED is authorized        for ProSe Direct Communication transmission using the UE context        received from MME;    -   The eNB may configure a UE in RRC_CONNECTED by dedicated        signaling with a mode 2 resource allocation transmission        resource pool that may be used without constraints while the UE        is RRC_CONNECTED. Alternatively, the eNB may configure a UE in        RRC_CONNECTED by dedicated signaling with a mode 2 resource        allocation transmission resource pool which the UE is allowed to        use only in exceptional cases and rely on mode-1 otherwise.

In Mode 1, a UE requests transmission resources from an eNodeB. TheeNodeB schedules transmission resources for transmission of schedulingassignment(s) and data.

-   -   The UE sends a scheduling request (D-SR or RA) to the eNodeB        followed by a BSR based on which the eNodeB can determine that        the UE intends to perform a D2D transmission as well as the        required amount resources.    -   In Mode 1, the UE needs to be RRC Connected in order to transmit        D2D communication.

For Mode 2, UEs are provided with a resource pool (time and frequency)from which they choose resources for transmitting D2D communication.

FIG. 8 schematically illustrates the Overlay (LTE) and the Underlay(D2D) transmission and/or reception resources. The eNodeB controlswhether the UE may apply Mode 1 or Mode 2 transmission. Once the UEknows its resources where it can transmit (or receive) D2Dcommunication, it uses the corresponding resources only for thecorresponding transmission/reception. In the example of FIG. 8, the D2Dsubframes will only be used to receive or transmit the D2D signals.Since the UE as a D2D device would operate in Half Duplex mode, it caneither receive or transmit the D2D signals at any point of time.Similarly, in the same figure, the other subframes can be used for LTE(overlay) transmissions and/or reception.

D2D discovery is the procedure/process of identifying other D2D capableand interested devices in the vicinity. For this purpose, the D2Ddevices that want to be discovered would send some discovery signals (oncertain network resources) and the receiving UE interested in the saiddiscovery signal will come to know of such transmitting D2D devices. Ch.8 of 3GPP TR 36.843 describes the available details of D2D Discoverymechanisms.

Transmission Procedure for D2D Communication

FIG. 10 schematically shows a transmission procedure for D2Dcommunication. The D2D data transmission procedure differs depending onthe resource allocation mode. As described above for mode 1 the eNBexplicitly schedules the resources for Scheduling assignment and D2Ddata communication. In the following the different steps of therequest/grant procedure is listed for model resource allocation:

-   -   Step 1 UE sends SR (Scheduling Request) to eNB via PUCCH;    -   Step 2 eNB grants UL resource (for UE to send BSR) via PDCCH,        scrambled by C-RNTI;    -   Step 3 UE sends D2D BSR indicating the buffer status via PUSCH;    -   Step 4 eNB grants D2D resource (for UE to send data) via PDCCH,        scrambled by D2D-RNTI.    -   Step 5 D2D Tx UE transmits SA/D2D data according to grant        received in step 4.

A Scheduling Assignment (SA) is a compact (low-payload) messagecontaining control information, e.g., pointer(s) to time-frequencyresources for the corresponding D2D data transmissions. The content ofthe SA is basically the grant received in Step 4 above. The exactdetails of the D2D grant and SA content are not fixed yet.

D2D Discovery

ProSe (Proximity based Services) Direct Discovery is defined as theprocedure used by the ProSe-enabled UE to discover other ProSe-enabledUE(s) in its proximity using E-UTRA direct radio signals via the PC5interface. FIG. 11 schematically illustrates a PC5 interface for deviceto device direct discovery, as described in 3GPP TS 23.303 V12.0.0,section 5.1.1.4 which is enclosed herein by reference.

Upper layer handles authorization for announcement and monitoring ofdiscovery information. For the purpose, UEs have to exchange predefinedsignals, referred to as discovery signals. By checking discovery signalsperiodically, a UE maintains a list of proximity UEs in order toestablish communication link when it is needed. Discovery signals shouldbe detected reliably, even in low Signal-to-Noise Ratio (SNR)environments. To allow discovery signals to be transmitted periodically,resources for Discovery signals should be assigned.

There are two types of ProSe Direct Discovery: open and restricted. Openis the case where there is no explicit permission that is needed fromthe UE being discovered, whereas restricted discovery only takes placewith explicit permission from the UE that is being discovered.

ProSe Direct Discovery can be a standalone service enabler in adiscovering UE, which enables the discovering UE to use information froma discovered UE for certain applications. As an example, the informationtransmitted in ProSe Direct Discovery may be “find a taxi nearby”, “findme a coffee shop”, “find me the nearest police station” and the like.Through ProSe Direct Discovery a discovery UE can retrieve neededinformation. Additionally, depending on the information obtained, ProSeDirect Discovery can be used for subsequent actions in thetelecommunication system, such as, for example, initiating ProSe DirectCommunication.

ProSe Direct Discovery Models

ProSe Direct Discovery is based on several discovery models. The modelsfor ProSe Direct Discovery are defined in 3GPP TS 23.303 V12.0.0,section 5.3.1.2 which is enclosed herein by reference:

Model a (“I am Here”)

Model A is also indicated as “I am here”, since the announcing UEbroadcasts information about itself, such as its ProSe ApplicationIdentities or ProSe UE Identities in the discovery message, therebyidentifying itself and communicating to the other parties of thecommunication system that it is available.

According to Model A two roles for ProSe-enabled UEs that areparticipating in ProSe Direct Discovery are defined. ProSe-enabled UEcan have the function of Announcing UE and Monitoring UE. An announcingUE announces certain information that could be used by UEs in proximitythat have permission to discover. A Monitoring UE monitors certaininformation of interest in proximity of announcing UEs.

In this model the announcing UE broadcasts discovery messages atpre-defined discovery intervals and the monitoring UEs that areinterested in these messages read them and process them.

Model B (“Who is There?”/“are You There?”)

This model defines two roles for the ProSe-enabled UEs that areparticipating in ProSe Direct Discovery:

-   -   Discoverer UE: The UE transmits a request containing certain        information about what it is interested to discover;    -   Discoveree UE: The UE that receives the request message can        respond with some information related to the discoverer's        request.

Model B is equivalent to “who is there/are you there” since thediscoverer UE transmits information about other UEs that would like toreceive responses from. The transmitted information can be, for example,about a ProSe Application Identity corresponding to a group. The membersof the group can respond to said transmitted information.

According to this model two roles for the ProSe-enabled UEs that areparticipating in ProSe Direct Discovery are defined: discoverer UE anddiscoveree UE. The discoverer UE transmits a request containing certaininformation about what it is interested to discover. On the other hand,the discoveree UE receives the request message can respond with someinformation related to the discoverer's request.

The content of discovery information is transparent to Access Stratum(AS), which does not know the content of discovery information. Thus, nodistinction is made in the Access Stratum between the various ProSeDirect Discovery models and types of ProSe Direct Discovery. The ProSeProtocol ensures that it delivers only valid discovery information to ASfor announcement.

The UE can participate in announcing and monitoring of discoveryinformation in both RRC_IDLE and RRC_CONNECTED state as per eNBconfiguration. The UE announces and monitors its discovery informationsubject to the half-duplex constraints.

Types of Discovery

FIG. 12 illustrates a diagram showing the IDLE and CONNECTED mode in thereception of discovery resources in D2D communication.

D2D communication may either be network-controlled where the operatormanages the switching between direct transmissions (D2D) andconventional cellular links, or the direct links may be managed by thedevices without operator control. D2D allows combininginfrastructure-mode and ad hoc communication.

Generally device discovery is needed periodically. Further D2D devicesutilize a discovery message signalling protocol to perform devicediscovery. For example, a D2D-enabled UE can transmit its discoverymessage and another D2D enabled UE receives this discovery message andcan use the information to establish a communication link. An advantageof a hybrid network is that if D2D devices are also in communicationrange of network infrastructure, network entity like eNB canadditionally assist in the transmission or configuration of discoverymessages. Coordination/control by the eNB in the transmission orconfiguration of discovery messages is also important to ensure that D2Dmessaging does not create interference to the cellular trafficcontrolled by the eNB. Additionally, even if some of the devices areoutside of the network coverage range, in-coverage devices can assist inthe ad-hoc discovery protocol.

At least the following two types of discovery procedure are defined forthe purpose of terminology definition used further in the description.

-   -   Type 1: A resource allocation procedure where resources for        announcing of discovery information are allocated on a non UE        specific basis, further characterized by:        -   The eNB provides the UE(s) with the resource pool            configuration used for announcing of discovery information.            The configuration may be signalled in SIB.        -   The UE autonomously selects radio resource(s) from the            indicated resource pool and announce discovery information.        -   The UE can announce discovery information on a randomly            selected discovery resource during each discovery period.    -   Type 2: A resource allocation procedure where resources for        announcing of discovery information are allocated on a per UE        specific basis, further characterized by:        -   The UE in RRC_CONNECTED may request resource(s) for            announcing of discovery information from the eNB via RRC.            The eNB assigns resource(s) via RRC.        -   The resources are allocated within the resource pool that is            configured in UEs for monitoring.

The resources are according to the type 2 procedure for exampleallocated semi-persistently allocated for discovery signal transmission.

In the case UEs are in RRC_IDLE modus, the eNB may select one of thefollowing options:

-   -   The eNB may provide a Type 1 resource pool for discovery        information announcement in SIB. UEs that are authorized for        Prose Direct Discovery use these resources for announcing        discovery information in RRC_IDLE.    -   The eNB may indicate in SIB that it supports D2D but does not        provide resources for discovery information announcement. UEs        need to enter RRC Connected in order to request D2D resources        for discovery information announcement.

For UEs in RRC_CONNECTED status, a UE authorized to perform ProSe DirectDiscovery announcement indicates to the eNB that it wants to perform D2Ddiscovery announcement. Then, the eNB validates whether the UE isauthorized for ProSe Direct Discovery announcement using the UE contextreceived from MME. The eNB may configure the UE to use a Type 1 resourcepool or dedicated Type 2 resources for discovery informationannouncement via dedicated RRC signalling (or no resource). Theresources allocated by the eNB are valid until a) the eNB de-configuresthe resource (s) by RRC signalling or b) the UE enters IDLE.

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type2 discovery resource pools as authorised. The eNB provides the resourcepool configuration used for discovery information monitoring in SIB. TheSIB may contain discovery resources used for announcing in neighbourcells as well.

Radio Protocol Architecture

FIG. 13 schematically illustrates a Radio Protocol Stack (AS) for ProSeDirect Discovery.

The AS layer interfaces with upper layer (ProSe Protocol). Accordingly,the MAC layer receives the discovery information from the upper layer(ProSe Protocol). In this context, the IP layer is not used fortransmitting the discovery information. Further, the AS layer has ascheduling function: the MAC layer determines the radio resource to beused for announcing the discovery information received from upper layer.In addition, the AS layer has the function of generating Discovery PDU:the MAC layer builds the MAC PDU carrying the discovery information andsends the MAC PDU to the physical layer for transmission in thedetermined radio resource. No MAC header is added.

In the UE, the RRC protocol informs the discovery resource pools to MAC.RRC also informs allocated Type 2 resource for transmission to MAC.There is no need for a MAC header. The MAC header for discovery does notcomprise any fields based on which filtering on Layer 2 could beperformed. Discovery message filtering at the MAC level does not seem tosave processing or power compared to performing filtering at the upperlayers based on the ProSe UE- and/or ProSe Application ID. The MACreceiver forwards all received discovery messages to upper layers. MACwill deliver only correctly received messages to upper layers.

In the following it is assumed that L1 indicates to MAC whether adiscovery messages has been received correctly. Further, it is assumedthat the Upper Layers guarantee to deliver only valid discoveryinformation to the Access Stratum.

Prior art solution for allocation of resources for discovery in D2Dsystems, do not allow determining a resource pattern or a configurationsuitable for allocating resources in a manner that is suitable for therequested D2D service. Specifically, based on the informationtransmitted by the D2D capable device according to common signalingprocedures, the base station could allocate the transmission resourcesfor a too short time period for allowing the UE to broadcast thecomplete discovery information. Consequently, the transmitting UE needsto request resources again, thereby leading to an increase of signalingoverhead into the LTE system.

Moreover, for example information on the content of discoveryinformation is transparent to the Access Stratum (AS). Therefore, nodistinction is made in the Access Stratum between the various ProSeDirect Discovery models and types of ProSe Direct Discovery and the basestation would not receive any information useful for determining themodel of discovery transmission and the type of preferred procedure forallocating discovery resources.

D2D Synchronization

The main task of synchronization is to enable the receivers to acquire atime and frequency reference. Such reference may be exploited for atleast two goals: 1) aligning the receiver window and frequencycorrection when detecting D2D channels and 2) aligning the transmittertiming and parameters when transmitting D2D channels. Following channelshave been defined in 3GPP so far for the purpose of synchronization

-   -   D2DSS D2D Synchronization Signal    -   PD2DSCH Physical D2D Synchronization Channel    -   PD2DSS Primary D2D Synchronization Signal    -   SD2DSS Secondary D2D Synchronization Signal

Furthermore the following terminology with respect to synchronizationwas agreed in 3GPP.

D2D Synchronization Source: A node that at least transmits a D2Dsynchronization signal.

D2D Synchronization Signal: A signal from which a UE can obtain timingand frequency synchronization

A D2D synchronization source can be basically an eNB or an D2D UE.

D2D synchronization could be seen as a procedure which is similar to LTEcell search. In order to allow both NW control and efficientsynchronization for partial/outside coverage scenarios, the followingprocedure is currently under discussion within 3GPP.

Receiver Synchronization

The ProSe enabled UE regularly searches for LTE cells (according to LTEmobility procedures) and for D2DSS/PD2DSCH transmitted by SS UEs.

If any suitable cell is found, the UE camps on it and follows the cellsynchronization (according to LTE legacy procedures).

If any suitable D2DSS/PD2DSCH transmitted by SS UEs are found, the UEsynchronizes its receiver to all incoming D2DSS/PD2DSCH (subject to UEcapabilities) and monitors them for incoming connections (SchedulingAssignments). It should be noted that the D2DSS transmitted by a D2DSynchronization Source which is an eNodeB shall be the Rel-8 PSS/SSS.D2D Synchronization Sources which are eNodeBs have a higher prioritythan D2D Synchronization Sources which are UEs.

Transmitter Synchronization

The ProSe enabled UE regularly searches for LTE cells (according to LTEmobility procedures) and for D2DSS/PD2DSCH transmitted by SS UEs;

If any suitable cell is found, the UE camps on it and follows the cellsynchronization for D2D signals transmission, the NW may configure theUE to transmit D2DSS/PD2DSCH following the cell synchronization.

If no suitable cell is found, the UE verifies if any of the incomingD2DSS/PD2DSCH may be relayed further (i.e., the max hop count has notbeen reached), then (a) if an incoming D2DSS/PD2DSCH that may be relayedfurther is found, the UE adapts its transmitter synchronization to itand transmits D2DSS/PD2DSCH accordingly; or (b) if an incomingD2DSS/PD2DSCH that may be relayed further is NOT found, the UE acts asindependent synchronization source and transmit D2DSS/PD2DSCH accordingto any internal synchronization reference.

Further details on the synchronization procedure for D2D can be found inTS 36.843.

SUMMARY OF THE INVENTION

One exemplary embodiment provides a transmitting terminal fortransmitting data to a receiving terminal over a direct link connectionin a communication system is given. The transmitting terminal is adaptedto determine the transmission timing of the direct link datatransmission in the communication system and comprises a receiving unitadapted to receive from the base station an uplink control informationmessage including a timing command for adjusting an uplink transmissiontiming value for data transmissions to the base station. A generatingunit is configured to generate direct link timing information, based onthe uplink transmission timing value used for uplink transmissions tothe base station, the direct link timing information being usable forgenerating a direct link transmission timing value for determining thetiming of the data transmission over the direct link. A transmittingunit transmits to the receiving terminal the generated direct linktiming information, the direct link timing information being usable atthe receiving terminal for generating a direct link reception timingvalue for determining the reception timing of data to be received on thedirect link from the transmitting terminal.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE FIGURES

In the following the exemplary embodiments will be described in moredetail in reference to the attached figures and drawings. Similar orcorresponding details in the figures are marked with the same referencenumerals.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3 shows exemplary subframe boundaries on a downlink componentcarrier as defined for 3GPP LTE (Release 8/9);

FIG. 4 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9);

FIGS. 5 and 6 show the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the downlink and uplink, respectively;

FIG. 7 is a schematic illustration showing a system including D2Dcapable user equipments;

FIG. 8 is a schematic illustration showing the overlay (LTE) and theUnderlay (D2D) transmission and reception resources in D2D subframes;

FIG. 9 illustrates the behavior regarding resource allocation in D2Dcommunication;

FIG. 10 schematically shows a transmission procedure for D2Dcommunication;

FIG. 11 shows a schematic representation of the PC5 interface for deviceto device direct discovery and a schematic representation of the RadioProtocol Stack for ProSe Direct Discovery;

FIG. 12 is a diagram showing the IDLE and CONNECTED mode in thereception of discovery resources according to an exemplary development;

FIG. 13 schematically illustrates a Radio Protocol Stack (AS) for ProSeDirect Discovery;

FIG. 14 illustrates a scheme for controlling transmission timing fortransmitting data from a transmitting UE to a receiving UE over a directlink connection;

FIG. 15 shows a transmitting/receiving user equipment according to anexemplary development.

FIG. 16 illustrates a scheme for controlling transmission timing fortransmitting data from a transmitting UE to a receiving UE over a directlink connection according to the configuration shown in FIG. 15;

FIG. 17 shows a scheme for controlling transmission timing fortransmitting data from a transmitting UE to a receiving UE over a directlink connection according to a further development.

DETAILED DESCRIPTION

The following paragraphs will describe various exemplary embodiments.For exemplary purposes only, most of the embodiments are outlined inrelation to a radio access scheme according to 3GPP LTE (Release 8/9)and LTE-A (Release 10/11/12) mobile communication systems, partlydiscussed in the Technical Background section above. It should be notedthat the exemplary embodiments may be advantageously used, for example,in a mobile communication system such as 3GPP LTE-A (Release 10/11/12)communication systems as described in the Technical Background sectionabove, but the exemplary embodiments are not limited to their use inthis particular exemplary communication networks.

The term “direct link” used in the claims and in the description is tobe understood as a communication link (communication channel) betweentwo D2D user equipments, which allows the exchange of data directlywithout the involvement of the network. In other words, a communicationchannel is established between two user equipments in the communicationsystem, which are close enough for directly exchanging data, bypassingthe eNodeB (base station). This term is used in contrast with “LTE link”or “LTE (uplink) traffic”, which instead refers to data traffic betweenuser equipments managed by the eNodeB.

The term “transmitting user equipment” or “transmitting terminal” usedin the claims and in the description is to be understood as a mobiledevice capable of transmitting and receiving data. The adjectivetransmitting is only meant to clarify a temporary operation. Thetransmitting user equipment in the following and for the purpose ofdiscovery transmission can be an announcing user equipment or adiscovering user equipment (discoverer). The term is used in contrast to“receiving user equipment” or “receiving terminal”, which refers to amobile device temporarily performing the operation of receiving data.The receiving user equipment in the following and for the purpose ofdiscovery transmission can be a monitoring user equipment or a Userequipment to be discovered (discoveree).

In the following, several examples will be explained in detail. Theexplanations should not be understood as limiting the invention, but asa mere exemplary embodiments to better understand the invention. Askilled person should be aware that the general principles as laid outin the claims can be applied to different scenarios and in ways that arenot explicitly described herein. Correspondingly, the following scenarioassumed for explanatory purposes of the various embodiments shall not belimiting as such.

The present invention is based on the observation that in a D2Dcommunication system the synchronization of transmission and receptionof data transmitted from a transmitting terminal to a receiving terminalover a direct link assumes an important relevance. Specifically it isimportant that the receiving terminal can set a reception window, morein particular the FFT window, in time for receiving data from thetransmitting terminal, which is as close as possible to the time atwhich the transmitting terminal transmits data over the direct linkconnection plus the propagation delay between the transmitting andreceiving terminal. If the data transmitted over the direct link is notreceived at the correct timing, i.e. the receiving FFT window is notpositioned at the correct timing, the SNR will decrease, thereby causinga deterioration of the performance of the data transmission. Inparticular for cases where the timing mismatch exceeds the cyclic prefixlength, i.e. the reception is out the CP, the decoding performance wouldbe significantly reduced, e.g. it might not be possible to correctlydecode the data. In addition, in order to reduce intra cellinterferences in the communication system, it would be advantageous ifthe data transmission over the direct link were synchronized with LTEdata transmission, i.e. LTE data and direct link data is received withthe same timing at the base station, or in other words with the datatraffic in uplink between the terminals and the base station.

FIG. 14 illustrates a possible scheme for controlling transmissiontiming for transmitting data from a transmitting UE (from now on UE1) toa receiving UE (from now on UE2) over a direct link connection. Asolution that allows reducing intra cell interference consists in using,at the transmitting UE, for the data transmission over the direct linkthe same uplink timing as used by the transmitting UE for uplink datatransmissions to the base station. The uplink timing is, as explainedbefore in section “time advance”, controlled by the eNB by means ofTiming advance (TA) commands based on which the UE1 can adjusts itsinternal timing advance value to an 11 bit value, called N_(TA) value.

According to the solution illustrated in FIG. 14, therefore, thetransmitting UE uses the LTE uplink timing also for D2D datatransmissions. Specifically, the N_(TA) value, which is used by the UE1for adjusting transmission timing for transmitting data to the basestation and over the direct link is also used as a basis forsynchronizing the t FFT windows of the receiving UEs, i.e. UE2.

Specifically, UE1 will maintain the 11 bit N_(TA) value which will bethen used for determining the timing advance with respect to thedownlink reception timing. A timing advance value is sent to thereceiving UEs, e.g. UE2 in this example, in a control message, alsoreferred to as scheduling assignment (SA) message, which is however 6bits. Therefore, the UE1 downsamples the 11 bit N_(TA) value for uplinktransmissions to 6 bits before transmitting same within the SA messageto the UE2. As an example of downsampling, the UE1 may transmit to theUE2 only the 6 most significant bits of the uplink N_(TA) value.

FIG. 14 shows different timings, represented on the horizontal lines forthe eNb, for the UE1 and for the UE2. In this example UE1 (transmittingUE) transmits data to UE2 (receiving UE) over the direct link. Thedownlink timing—i.e. the point of time where the eNB signaling includingthe TA command for uplink timing adjustment—received at UE1 is indicatedwith Rx_(eNB)@UE1.

The UE1 downsamples the N_(TA) value determined in the UE based on theTA commands received from the eNb and the autonomous timing adjustmentfunction as described before and transmits a direct link SchedulingAssignment (SA) message including the downsampled N_(TA) value fordirect link communication over the direct link (PC5 interface), which ismonitored/received by UE2. The direct link SA message is received at UE2at Rx_(D2D_)SA@ UE2.

According to this configuration, the direct link data will betransmitted from UE1 over direct link with a timing advance adjustedbased on the 11 bit N_(TA) value, or in other words with the uplinktiming (Tx_(LTE_)UE1=Tx_(D2D_)UE1). The D2D data or the direct link datatransmitted by UE1 is received by the UE2, at the timeRx_(D2D_)data@UE2. On the other hand UE2 calculated the time at whichthe data from the UE1 have to be expected based on the downsampled 6 bitN_(TA) value received within the SA message. The timing advance valuetransmitted to the UE2 in the SA message is thus not the same as thetiming advance value used by UE1 but only an approximation thereof.

This solution may be problematic at the present time since, based oncurrent technologies, UE2 cannot position its reception window in timecorrectly, thereby degrading the decoding performance and decreasing theSNR. Nonetheless, it is anticipated that future advances may allow toobtain a good performance also is the timing advance used by UE2 is onlyan approximation of that used by the UE1, thereby mitigating theaforementioned problems.

In conclusion, the solution described above allows to reduce intercarrier interference because the D2D data are transmitted using the sametiming advance for direct link communication and for the legacy LTEuplink communications. However, at present the receiving UE (UE2) cannot adjust its reception FFT window efficiently because the 6 bitsN_(TA) value sent by the UE1 within the SA message is only anapproximation of the 11 bit N_(TA) value used by UE1 for transmittingD2D data.

The problems related to the solution described with reference to FIG. 14are solved by providing a transmitting UE, which uses, for direct linkdata transmissions, the same timing advance value used by the receivingUE for setting the reception FFT window for D2D data.

A transmitting/receiving user equipment 500 according to this furtherdevelopment is shown in FIG. 15. The user equipment or a terminal 500 iscapable of transmitting data to a receiving terminal over a direct linkconnection in a D2D communication system. The transmitting terminal 500is configured to determine the transmission timing of the direct linkdata transmission in the communication system. To this end thetransmitting UE 500 comprises a reception or receiving unit (540) thatcan receive from a base station an uplink message including a timingadvance command. The timing advanced command may be a MAC controlelement and can be used by the UE 500 for adjusting an uplinktransmission timing value for data transmissions to the base station.The received TA command is input in to a generating unit 570 eitherdirectly or through a control unit and the generating unit 570generates, based on the input TA command an uplink transmission timingvalue for controlling transmission timing in uplink to the base station510.

At the same time, the generating unit 570 generates, based on the uplinktransmission timing value, direct link timing information. The directlink timing information is used by the transmitting terminal 500 inorder to determine the timing of the data transmission to the receivingterminal over the direct link.

The transmitting terminal 500 transmits by means of a transmitting unit560, the generated direct link timing information to the receivingterminal 500. The transmitted direct link timing information can be usedat the receiving terminal for generating a direct link reception timingvalue. Advantageously, the timing for direct link data transmissiondetermined at the transmitting terminal is the same as the direct linkreception timing value calculated at the receiving terminal.

FIG. 16 illustrates scheme for controlling transmission timing fortransmitting data from a transmitting UE (UE1) to a receiving UE (UE2)over a direct link connection according to the configuration shown inFIG. 15. The UE1 uses a TA value for direct link transmission which isthe same TA value transmitted in the direct link SA to UE2. Therefore,the reception window determined by UE2 using the direct link TA value(TA_(D2D_)UE1) can be adjusted to match the transmission timingRx_(D2D_)data@UE2 of D2D data.

In an exemplary implementation of the solution described above the UE1generates and maintains, based on e.g. the received uplink TA commandsfrom eNB, an 11 bits N_(TA) value for adjusting the transmission timingfor the legacy LTE uplink transmissions to the base station. At the sametime, the UE1 downsamples the 11 bits N_(TA) value in order to create a6 bits direct link timing information. The direct link timinginformation may be for instance created by taking the 6 most significantbits of the uplink N_(TA) value maintained for LTE uplink operation. Thedirect link timing information will then be transmitted, for exampleincorporated in the direct link SA message, to UE2 on one hand. On theother hand, UE1 generates based on the direct link timing information an11 bits direct link N_(TA) value. The 11 bits direct link N_(TA) valuemay be for instance created by prepending a series of zeros to thedirect link timing information. Similarly, UE2 will extract from thereceived direct link SA message the 6 bits direct link timinginformation and recover, based thereon, the 11 bits direct link N_(TA)value by prepending a series of zeros to the signaled direct link timinginformation. Accordingly, the direct link N_(TA) value used by UE2 foradjusting the reception FFT window will be the same as that timingadvance value used by the UE1 for data transmission over the directlink. As further shown in FIG. 16 the UE2 applies the generated N_(TA)value to the reception timing of the SA message.

The idea above can be explained by means of the following example. Ifthe 11 bits N_(TA) value for LTE uplink data transmissions to the basestation is N_(TA_UPLINK)=11011011001, the downsampled direct link timinginformation calculated by considering the 6 MSB will be 110110. Indownsampling the information carried out by UE1 the first bits will belost and the direct link transmission timing value will be given byN_(TA_D2D)=11011000000. Similarly, the receiving UE (UE2) will receivewith the SA message the direct link timing information conveying thevalue to 110110. Based thereon, UE2 can generate a direct link receptiontiming value by prepending to the received value a series of zero. Thedirect link reception timing value will be N_(TA_D2D)=11011000000.

The above is only an example to explain how the general concepts of theinvention can be applied in a specific implementation. It has however tobe clear that this example is not limiting. For instance, the uplinktransmission timing value may be shorter or longer than 11 bits.Similarly the direct link timing information may be generated by meansof a procedure different than the downsampling. Although reference ismade to a direct link timing information having 6 bits, the direct linktiming information may also be longer. Same also applies to the directlink transmission timing value.

The timing advance values generated at the UE1 and at the UE2 fordetermining the transmission and reception timing for D2D datarespectively are thus the same and this allows the receiving terminal toset a reception FFT window that matches the transmission timing of D2Ddata. Clearly the direct link timing value calculated at the UE1 and UE2will not be the same as the uplink transmission timing value for legacyLTE uplink transmission but only an approximation thereof. Thisdiscrepancy may at the present time in light of the present technologiesgenerate, under certain conditions, inter-carrier interference for LTEuplink transmission at the eNB reception site because the uplink timingfor transmitting data to the eNb is different from the transmissiontiming for D2D data transmission.

A further development that allows reducing inter-carrier interferenceconsists in a configuration implementing both the solution describedwith reference to FIG. 14 and the solution described with respect toFIGS. 15 and 16.

According to this further development the base station determines whichscheme will be used. Specifically, the base station 510 of the directlink communication system, which is adapted to control the time fordirect link data transmission in the communication system, comprises areceiving unit adapted to receive from the transmitting terminal 500 aresource request message for allocation of resources for uplink datatransmission. The base station generates, at a generating unitconfiguration information which is transmitted by means of atransmitting unit in the base station to the transmitting UE 500 or UE1.The UE1 uses the received configuration information for performingcontrol of the transmission timing over the direct link.

In particular, at the transmitting unit 500, the receiving unit 540receives the configuration information from the base station.Subsequently, in accordance with the received configuration information,the transmitting UE 500, for example at the transmitting unit 560,selects (1) the generated direct link timing information or (2) theuplink transmission timing value used for uplink transmission to thebase station. Based on the selection, the transmitting UE controlstransmission timing over the direct link.

In case (1), the transmitting UE will generate a direct linktransmission timing value as described with reference to the FIGS. 15and 16, thereby preferring a scheme that assures a good decodingperformance but increases inter-frame interference. This solution couldbe used if the base station implements ICI mitigation techniques, suchas guard bands or the like, in order to mitigate ICI. This solutioncould also be used if the base station does not consider necessary toreduce interference.

In case (2), the transmitting UE will use the legacy LTE uplinktransmission timing for uplink transmission to the base station also fortransmitting data to the receiving UE over the direct link. The D2Dtransmission timing will, in this case, be aligned with the LTE uplinktransmission timing, thereby keeping the ICI for uplink transmission ofdata to the base station low. The trade-off of this transmission schemeis that the reception FFT window for the D2D data transmitted by thetransmitting UE will not be efficiently adjusted. Such solution can beused in cases where the protection of LTE uplink transmission due to theavoidance of additional inter-carrier interference caused by direct linkdata transmission is of more importance than the D2D performance. Forexample in cases where eNB has no means to deploy ICI mitigationtechniques like power control or guard bands such solution might beadvantageous from network point of view.

According to a further development, which would solve the problem ofreducing interference and obtain a good decoding performance, thetransmitting UE may include in direct link SA message the uplink timingadvance value N_(TA) generated e.g. based on the TA commands receivedfrom the base station for adjusting the transmission timing of LTEuplink transmissions. In other words, according to this development thedirect link SA message includes the 11 bit N_(TA) value, which will besignalled to the receiving UE instead of a downsampled 6 bits uplinktransmission timing. Accordingly, the same timing advance value will beused for D2D data transmission and reception, thereby allowing thereceiving UE to exactly adjust the FFT transmission window. Furthermore,since the D2D data transmission timing is the same as the uplink datatransmission timing to the base station, ICI to LTE uplink transmissioncan be minimized. This solution requires, however to transmit to thereceiving UE an SA message including a TA field of 11 bits, therebyincreasing signalling.

According to a further development, the transmitting UE may select at acontrol unit 590, independently from the base station, whichtransmission scheme is to be used for the D2D transmission timing.

The transmitting terminal includes a control unit 590 which is, amongothers, adapted to select based on a predefined selection criterion,whether the timing for the transmission of data over the direct linkshould be adjusted (1) based on the generated direct link timinginformation or (2) based on the uplink transmission timing informationvalue used for uplink transmission to the base station. The two optionsare the same, which have been described previously in text and will notbe described again.

The selection criterion may comprise comparing a cyclic prefix lengthfor uplink transmissions to the base station and a cyclic prefix lengthfor transmissions on the direct link or determining whether thetransmitting terminal is in a connected or idle state.

Specifically, in case that cyclic prefix length for uplink transmissionto the base station (LTE WAN) is different than the cyclic prefix lengthfor direct link transmission (D2D transmission), the ICI in the cellwill be high and the base station will need to implement measures tomitigate interference, such as band guards and the like. In this case,since guard bands for reducing ICI are already configured, thetransmitting UE may decide to choose scheme (1) and use the direct linktiming information signalled to the receiving UE for adjusting thetransmission timing of D2D data transmission. This solution allows thereceiving UE to exactly adjust the FFT reception window, therebyobtaining good decoding performance at the expense of higherinterference. The higher interference on the uplink transmission willthen be mitigated through the guard bands for example.

On the contrary, the transmitting UE may determine the direct linktransmission timing according to scheme (2), in the case that the cyclicprefix length for uplink transmission to the base station (LTE WAN) andfor direct link transmission (D2D transmission) are the same. In thiscase the base station may not implement or use any measure formitigating ICI and therefore it may be preferred the transmission timingcontrol scheme for D2D transmission that allows reducing the inter-frameinterference. To this end, the transmitting UE may use the LTE uplinktransmission timing value for determining the timing of the datatransmission over the direct link.

Finally, as an further exemplary embodiment if the transmitting UE isnot able to determine the cyclic prefix length for LTE WAN, same cancontrol transmission timing over the direct link according to scheme(1).

Alternatively or in addition, the transmitting UE may decide whichscheme is to be used for controlling direct link transmission timingbased on the RRC state. If the transmitting UE is in a RCC_CONNECTEDstate, the transmitting UE may use the direct link timing informationfor generating a direct link transmission timing value, which will thenbe used for determining the timing of the data transmission over thedirect link (scheme 2). Otherwise, if the transmitting UE is in anRCC_IDLE state, it may use a direct link transmission timing advancevalue which is equal to 0. Specifically, if the transmitting UE is inidle mode, it will not receive from the base station any TA commands asit has no RRC connection to the base station and therefore it will nothave any uplink transmission timing advance value. Therefore thetransmitting UE in RRC IDLE mode cannot align the direct linktransmission timing to the LTE uplink transmission timing. As aconsequence according to an exemplary embodiment the transmitting UE inRRC_IDLE uses the downlink timing, i.e. the timing when SA message isreceived, for transmission of data over the direct link.

According to a further embodiment the data reception FFT window positionis determined based on the reception timing of the SA message.Specifically, the direct link timing information included in the SAmessage received at the receiving UE from the transmitting UE is used asthe reference timing for the positioning of the reception FFT window.More in particular the receiving UE applies the timing advance valuegenerated based on the received direct link timing information withinthe SA message to the SA reception timing. Accordingly, the receiving UEmay include a storing unit adapted to store, for instance in a variable,the reception timing of the SA message from the transmitting UE. Thestored reception timing will be then used to compute the position of thereceiving FFT window for the D2D data reception. AlternativelyD2DSS/PD2DSCH can be used as timing reference. FIG. 17 shows how theposition of the receiving window for D2D data can be set according themethod above.

According to another embodiment the transmitting terminal, which iscapable of data transmissions over the direct link may be configuredwith a separate Timing Advance Timer and/or respectively TAT value forD2D. This Timing Advance Timer (TAT) value maybe for example configuredto infinity. Such a choice would imply as a consequence that atransmitting UE can always transmit data over the direct link, even forcases where no LTE uplink transmission to the base station is allowedsince the TAT is expired for LTE uplink transmissions. In such a casethe transmitting UE may determine the transmission timing for the directlink data transmission according to the last available N_(TA) valuestored in the storing unit of the transmitting terminal.

Alternatively the transmitting UE may use a timing advance equal to zerofor transmission timing of direct link data. In other words, thetransmitting UE may use the same transmission timing used fortransmission of the SA message or control information message over thedirect link.

According to another embodiment the transmitting terminal, which iscapable of data transmissions over the direct link may also follow theTiming Alignment Timer used for LTE uplink transmission timing control.More in particular when TAT timer has expired and UE is not allowed tomake any LTE uplink transmissions to the base station, the transmittingUE is also not allowed to make direct link data transmissions and/ordiscovery announcements over the direct link. The TAT timer needs to berestarted first by reception of a TA command. For resource allocationmode 1 the transmitting UE should trigger and perform the random accessprocedure before sending any uplink transmissions to the base station,e.g. dedicated scheduling request on PUCCH, or any data transmissionover the direct link. Similarly according to another embodiment thetransmitting UE, when being configured to use resource allocation mode 2for D2D data communication may trigger or perform the random accessprocedure before sending scheduling assignment message or data over thedirect link in case the Timing Alignment Timer has been expired.

In summary and according to an embodiment, a transmitting terminal fortransmitting data to a receiving terminal over a direct link connectionin a communication system is given. The transmitting terminal is adaptedto determine the transmission timing of the direct link datatransmission in the communication system and comprises a receiving unitadapted to receive from the base station an uplink control informationmessage including a timing command for adjusting an uplink transmissiontiming value for data transmissions to the base station. A generatingunit is configured to generate direct link timing information, based onthe uplink transmission timing value used for uplink transmissions tothe base station, the direct link timing information being usable forgenerating a direct link transmission timing value for determining thetiming of the data transmission over the direct link. A transmittingunit transmits to the receiving terminal the generated direct linktiming information, the direct link timing information being usable atthe receiving terminal for generating a direct link reception timingvalue for determining the reception timing of data to be received on thedirect link from the transmitting terminal.

In the transmitting terminal the generating unit may be adapted todownsample the uplink transmission timing information value used foruplink transmissions to the base station, the direct link timinginformation being the downsampled uplink transmission timing value. Thedownsampled uplink transmission timing value may comprise the n mostsignificant bits of the uplink transmission timing information valueused for uplink transmission to the base station, n being a predefinedvalue.

Further, the timing of the data transmission over the direct link may begiven by the a direct link transmission timing value, and the directlink transmission timing value may be equal to the direct link receptiontiming value generated at a receiving terminal for determining thereception timing of data to be received on the direct link.

In the transmitting terminal the timing of the data transmission overthe direct link may be given by the uplink transmission timinginformation value used for uplink transmissions to the base station.

According to a further advantageous development, the receiving unit inthe transmitting terminal is further adapted to receive configurationinformation from the base station, and the transmitting unit isconfigured to use the generated direct link transmission timing valuetiming information or the received downlink uplink timing informationvalue for scheduling controlling transmission timing over the directlink in accordance with the received configuration information.

The transmitting terminal may further include a control unit adapted toselect, based on a predefined selection criterion whether the uplinktransmission timing information value used for uplink transmission tothe base station or the generated direct link transmission timing valuetiming information is to be used as the transmission timing over thedirect link for transmitting data over the direct link.

Advantageously, the selection criterion may comprise (1) comparing the acyclic prefix length for uplink transmissions to the base station andthe a cyclic prefix length for transmissions on the direct link; or (2)determining whether the transmitting terminal is in a connected or idlestate.

In the transmitting terminal the direct link timing information isgenerated based on the reception timing of the control informationmessage and on the uplink transmission timing value for datatransmissions to the base station.

An advantageous embodiment refers to a base station for use in a directlink communication system, the base station being adapted to control thetime scheduling for direct link data transmission in the communicationsystem. The base station comprises a receiving unit adapted to receivefrom a transmitting terminal a resource request message for allocationof resources for uplink data transmission. A generating unit is adaptedto generate configuration information for configuring, by thetransmitting terminal, timing information for scheduling controllingtransmission timing over the direct link. A transmitting unit transmitsthe configuration information to the transmitting terminal.

A further advantageous embodiment refers to a receiving terminal forreceiving data from a transmitting terminal over a direct linkconnection in a communication system. The receiving terminal comprises areceiving unit adapted to receive from the transmitting terminal directlink timing information generated at the transmitting terminal based onuplink transmission timing value used for uplink transmissions to thebase station. A generating unit generates a direct link reception timingvalue based on the received direct link timing information. Thereceiving unit controls the reception timing of data to be received onthe direct link from the transmitting terminal on the generated directlink reception timing value.

In the receiving terminal the direct link timing information is adownsampled uplink transmission timing value, and the generating unit isconfigured to prepend to the downsampled timing information a predefinednumber of zero bits.

According to an advantageous embodiment, the direct link receptiontiming value is equal to a direct link transmission timing valuegenerated at a transmitting terminal for determining timing of the datatransmission over the direct link.

A further advantageous embodiment refers to a communication method forcontrolling transmission timing of direct link data transmission by atransmitting terminal in a communication system. The method comprisesthe steps of:

at a receiving unit receiving from the base station an uplink controlinformation message including a timing command for adjusting an uplinktransmission timing value for data transmissions to the base station;

at a generating unit generating direct link timing information, based onthe uplink transmission timing value used for uplink transmissions tothe base station, the direct link timing information being usable forgenerating a direct link transmission timing value for determining thetiming of the data transmission over the direct link; and

at a transmitting unit transmitting to the receiving terminal thegenerated direct link timing information, the direct link timinginformation being usable at the receiving terminal for generating adirect link reception timing value for controlling the reception timingof data to be received on the direct link from the transmittingterminal; and

at a transmitting unit transmitting to the receiving terminal the dataover the direct link with the generated direct link transmission timingvalue transmission timing determined by the generated direct link timinginformation.

The communication method may further comprise the step of downsamplingthe received uplink transmission timing value used for uplinktransmissions to the base station, the direct link timing informationbeing generated based on the downsampled uplink transmission timingvalue. The downsampled timing information may comprise, as an example,the n most significant bits of the uplink transmission timing value, nbeing a predefined value.

In the communication method described above, the timing of the datatransmission over the direct link is given by the direct linktransmission timing value, and wherein the direct link transmissiontiming value is equal to the direct link reception timing valuegenerated at a receiving terminal for determining the reception timingof data to be received on the direct link.

The timing of the data transmission over the direct link may be given bythe uplink transmission timing information value used for uplinktransmissions to the base station.

Advantageously, the communication method as described above furthercomprises:

receiving from a base station configuration information, theconfiguration information being preferably included in the controlinformation, and

controlling transmission timing over the direct link based on thegenerated direct link transmission timing value or on the uplinktransmission timing value in accordance with the received configurationinformation.

This method may for example select, at a selecting unit, based on apredefined selection criterion whether the uplink transmission timingvalue or the direct link transmission timing value is to be used forcontrolling transmission timing of direct link data transmission.

The selection criterion may advantageously comprise (1) comparing adownlink cyclic prefix length for uplink transmissions to the basestation and a cyclic prefix length for transmissions on the direct link;or (2) determining whether the transmitting terminal is in a connectedor idle state.

A further advantageous embodiment refers to a communication method forcontrolling transmission timing of direct link data transmission by areceiving terminal in a communication system. The method comprises thesteps of

at a receiving unit receiving, from a transmitting terminal, direct linktiming information generated at the transmitting terminal based onuplink transmission timing value used for uplink transmissions to thebase.

at a generating unit generating a direct link reception timing valuebased on the received direct link timing, and

controlling, at the receiving unit, the reception timing of data to bereceived on the direct link from the transmitting terminal based on thegenerated direct link reception timing.

This communication method may further comprise the step of prepending,at the generating unit, a predefined number of zero bits to the directlink timing information if the direct link timing information isgenerated based on a downsampled uplink transmission timing value.

A further advantageous embodiment refers to a communication method forcontrolling, by a base station, transmission timing of direct link datatransmission in a communication system and comprising:

at a receiving unit receiving from a transmitting terminal a resourcerequest message for allocation of resources for uplink data transmissionto the base station;

generating, at a generating unit, configuration information forconfiguring, by the transmitting terminal, timing information forcontrolling transmission timing over the direct link, and

at a transmitting unit transmitting the generated the configurationinformation.

Another aspect of the invention relates to the implementation of theabove described various embodiments and aspects using hardware andsoftware. In this connection the invention provides a user equipment(mobile terminal) and a eNodeB (base station). The user equipment isadapted to perform the methods described herein. Furthermore, the eNodeBcomprises means that enable the eNodeB to evaluate the IntelligentPlatform Management Interface (IPMI) set quality of respective userequipments from the IPMI set quality information received from the userequipments and to consider the IPMI set quality of the different userequipments in the scheduling of the different user equipments by itsscheduler.

It is further recognized that the various embodiments of the inventionmay be implemented or performed using computing devices (processors). Acomputing device or processor may for example be general purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments of the invention may individually or in arbitrarycombination be subject matter to another invention.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

What is claimed is:
 1. A communication apparatus configured fordevice-to-device (D2D) communication, comprising: a receiver which, inoperation, receives control information indicating an uplink TimingAdvance value from a base station, the uplink Timing Advance value beingused to adjust an uplink transmission timing to the base station, and atransmitter which, in operation, transmits direct link data and directlink control information including a direct link Timing Advanceindication to another communication apparatus, wherein the direct linkdata and the direct link control information are not transmitted by thetransmitter in a case where a timing alignment timer (TAT) used for anuplink transmission to the base station has expired.
 2. Thecommunication apparatus according to claim 1, wherein the direct linkTiming Advance indication is generated by the communication apparatusbased on the uplink Timing Advance value.
 3. The communication apparatusaccording to claim 1, wherein the direct link Timing Advance indicationis generated by the communication apparatus by setting bits of thedirect link Timing Advance indication to zeros when the communicationapparatus is in a transmission mode which schedules resourcesautonomously by the communication apparatus.
 4. The communicationapparatus according to claim 1, wherein the direct link Timing Advanceindication is generated by the communication apparatus based on theuplink Timing Advance value when the communication apparatus is in anRRC_CONNECTED state, and the direct link data is generated by thecommunication apparatus by setting the direct link data to zeros whenthe communication apparatus is in an RRC_IDLE state.
 5. Thecommunication apparatus according to claim 1, wherein the direct linkdata is transmitted to the other communication apparatus based on adirect link transmission timing according to the direct link TimingAdvance indication.
 6. A communication method performed by acommunication apparatus configured for device-to-device (D2D)communication, the communication method comprising: receiving controlinformation indicating an uplink Timing Advance value from a basestation, the uplink Timing Advance value being used to adjust an uplinktransmission timing to the base station, and transmitting direct linkdata and direct link control information including the direct linkTiming Advance indication to another communication apparatus, whereinthe direct link data and the direct link control information are nottransmitted by the communication apparatus in a case where a timingalignment timer (TAT) used for an uplink transmission to the basestation has expired.
 7. The communication method according to claim 6,wherein the direct link Timing Advance indication is generated by thecommunication apparatus based on the uplink Timing Advance value.
 8. Thecommunication method according to claim 6, wherein the direct linkTiming Advance indication is generated by the communication apparatus bysetting bits of the direct link Timing Advance indication to zeros whenthe communication apparatus is in a transmission mode which schedulesresources autonomously by the communication apparatus.
 9. Thecommunication method according to claim 6, wherein the direct linkTiming Advance indication is generated by the communication apparatusbased on the uplink Timing Advance value when the communicationapparatus is in an RRC_CONNECTED state, and the direct link data isgenerated by the communication apparatus by setting the direct link datato zeros when the communication apparatus is in an RRC_IDLE state. 10.The communication method according to claim 6, wherein the direct linkdata is transmitted to the other communication apparatus based on adirect link transmission timing according to the direct link TimingAdvance indication.
 11. A communication apparatus configured fordevice-to-device (D2D) communication, comprising: a receiver which, inoperation, receives direct link control information including a directlink Timing Advance indication from another communication apparatus, andcircuitry which, in operation, sets a reception timing according to thedirect link Timing Advance indication to receive direct link data,wherein the direct link data and the direct link control information arenot transmitted from the other communication apparatus in a case where atiming alignment timer (TAT) used for an uplink transmission to a basestation has expired.
 12. The communication apparatus according to claim11, wherein the direct link Timing Advance indication is generated bythe other communication apparatus based on an uplink Timing Advancevalue, the uplink Timing Advance values being used to adjust an uplinktransmission timing to the base station.
 13. The communication apparatusaccording to claim 11, wherein the direct link Timing Advance indicationis generated by the other communication apparatus by setting bits of thedirect link Timing Advance indication to zeros when the othercommunication apparatus is in a transmission mode which schedulesresources autonomously by the other communication apparatus.
 14. Thecommunication apparatus according to claim 11, wherein the direct linkTiming Advance indication is generated by the other communicationapparatus based on an uplink Timing Advance value when the othercommunication apparatus is in an RRC_CONNECTED state, and the directlink data is generated by the other communication apparatus by settingthe direct link data to zeros when the other communication apparatus isin an RRC_IDLE state.
 15. The communication apparatus according to claim11, wherein the direct link data is transmitted to the othercommunication apparatus based on a direct link transmission timingaccording to the direct link Timing Advance indication.
 16. Acommunication method performed by a communication apparatus configuredfor device-to-device (D2D) communication, the communication methodcomprising: receiving direct link control information including a directlink Timing Advance indication from another communication apparatus, andsetting a reception timing according to the direct link Timing Advanceindication to receive direct link data, wherein the direct link data andthe direct link control information are not transmitted from the othercommunication apparatus in a case where a timing alignment timer (TAT)used for an uplink transmission to a base station has expired.
 17. Thecommunication method according to claim 16, wherein the direct linkTiming Advance indication is generated by the other communicationapparatus based on an uplink Timing Advance value, the uplink TimingAdvance values being used to adjust an uplink transmission timing to thebase station.
 18. The communication method according to claim 16,wherein the direct link Timing Advance indication is generated by theother communication apparatus by setting bits of the direct link TimingAdvance indication to zeros when the other communication apparatus is ina transmission mode which schedules resources autonomously by the othercommunication apparatus.
 19. The communication method according to claim16, wherein the direct link Timing Advance indication is generated bythe other communication apparatus based on an uplink Timing Advancevalue when the other communication apparatus is in an RRC_CONNECTEDstate, and the direct link data is generated by the other communicationapparatus by setting the direct link data to zeros when the othercommunication apparatus is in an RRC_IDLE state.
 20. The communicationmethod according to claim 16, wherein the direct link data istransmitted to the other communication apparatus based on a direct linktransmission timing according to the direct link Timing Advanceindication.